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Brakes
Brakes are used to stop a bicycle. As cycle technology has improved through time, various new braking technologies have replaced earlier solutions. History Early bicycles such as the high wheeled penny-farthing bikes had no brakes as we would recognize them. The machine was a fixed gear bicycle, and a rider could reduce speed by reversing the thrust on the pedals. Alternativelty, a rider needing to stop quickly had to jump off the bike as it was moving. Unsurprisingly this led to many accidents, some of them fatal. This limited the appeal of cycling, mostly to young and adventurous men. The 1870s saw the development of the "safety bicycle" which is much closer in appearance to a modern bicycle. It featured two wheels of equal size, initially with solid rubber tires. The braking system these bicycles used was often a simple leather pad which pressed against the top of the tire. This was driven by a rod attached to a lever on the handlebar. There was no rear brake, although with no free wheel, back-pedalling was an option. This was undoubtedly a big improvement on having no brakes at all, but it was not very powerful and had the big drawback that it was almost useless in wet weather. Along with the introduction of the pneumatic tire came the next advance in bicycle braking around the 1890s, the invention of the rim brake. This is the most common brake found on modern bicycles. Track bicycles, however, which are ridden at top speed continuously, continue to be built with no brakes; since they are fixed gear bicycles, braking on these bikes is still achieved only by reversing the force on the pedals. This is not a disadvantage for the very specialized manner in which these bicycles are ridden, and the reduction in weight is advantageous for performance. One of the most recent developments in bicycle braking technology is the use of hydraulics to transfer power from the brake lever to braking mechanism. Hydraulic rim and disc brakes are available, which typically give better feedback and increased power when compared to cable-operated alternatives. Variations Rim brakes See full article: Rim Brakes Disc brakes See full article: Disc Brakes Hub brakes Hub brakes are drum brakes that have their mechanism enclosed within the hub of the wheel, and are usually fitted to the back wheel. Because they are enclosed, hub brakes are completely unaffected by the weather. Some types of hub brake are operated by cables and levers, in the same way as rim and disc brakes. Other types are operated by the rider turning the pedals backwards. These are known as "back pedaling brakes", or "coaster brakes". Hub brakes are used mainly on utility bicycles, and also on some tandems used in mountains. In the tandem use, the drum is not intended to stop the bike. Instead they are used to keep the speed down on long downhill sections where extended use of rim brakes can cause overheating, similar to the use of disc brakes on tandems, discussed above. In addition to being impervious to changes in the weather, hub brakes have the advantage of needing very little regular maintenance, especially the back-pedaling type. Although hub brakes go for extended periods without maintenance, often their entire lifetime, they will eventually need to be dismantled and re-greased, usually by a professional, and sometimes they break and need repair. When hub brakes do require maintenance, it is far more complicated than other braking systems. Hub brakes are also heavier than other types of bicycle brake. Coaster brakes are not compatible with derailleur gears, where the freewheel built into the gear cluster on the rear wheel prevents back pedaling. Coaster brakes are also, by their basic design, inherently much less powerful than other braking systems, for the simple reason that they can only be installed on the rear wheel, which can provide much less braking force before skidding than the front wheel can. Braking Technique Effective use of a bicycle brake is highly counter-intuitive. The casual rider will at first avoid using the front brake, due to the unsettling feeling of "toppling up", or fear of being sent flying over the handlebars. However, the most effective technique is to use the front brake almost exclusively. There are several exceptions where the rear brake is preferred; these are listed below. In any stop, the rider should shift their weight toward the rear and use their arms to brace against the deceleration. During braking (either with the front or rear brake), the bike deceleration causes a transfer of weight to the front wheel. This means that the front wheel has a greater normal force pressing it against the ground, and the back wheel nearly none. Therefore, the front wheel can generate more frictional braking force than the back wheel before locking up and skidding. It is nearly impossible to lock the front wheel while braking. In any conditions and especially in wet conditions or going downhill, the rear brake can exert relatively little braking force before the wheel locks and starts skidding. A skidding rear wheel can lead to dangerous, uncontrollable bicycle movements eventually resulting in the cyclist falling on the ground. In an emergency stop, it is important to grab the front brake and press it hard to stop in the minimum possible distance. The rider should shift their weight as far to the rear as possible. Maximum deceleration is accomplished by maintaining enough pressure on the front brake such that that the rear wheel is barely touching the ground, just before flipping over the handlebars. In the real world this is not practical. Instead, use light pressure on the back wheel, hard pressure on the front. The back wheel is primarily useful as an indicator—when it starts to skid, reduce the pressure to both brakes to prevent flipping over the front wheel, then increase both again. Incidentally, on tandems, with their greater weight and long wheelbase, it is virtually impossible for heavy front braking to cause the machine to flip. There are a few special situations where limited use of the front brake, and heavier involvement of the rear brake is advisable: * Slippery surfaces. It is nearly impossible to recover from a front-wheel skid, so on surfaces like wet pavement, mud, snow, or ice, when skidding is likely, reduced speed and use of the rear brake is preferred. * Bumpy surfaces. If the front wheel comes off of the ground, braking will stop it completely. Coming down on a stopped front wheel is very dangerous. * Front flat tire. Braking the front wheel when the tire is flat could cause the tire to come off of the rim, which is more likely to cause a crash. * Broken cable, other mechanical failure. When the front brake fails, the only braking force can come from the rear brake. Manufacturers Common brake system manufacturers: * Avid * Campagnolo * Hayes * Hope * Magura * Shimano See Also * Wikipedia: Bicycle Brake Systems * Improving Brakes External links * Braking and Turning your Bicycle * Bicycle Repair: Adjusting brakes Category:Components Category:Brakes de:Bremsen